Today's fiber optic based networks use transceivers at the interface between electronics and the optical signals that propagate on the optical fiber. A transceiver is generally used to convert between electronic data and optical signals that are transmitted via an optical fiber. A transceiver contains within it the basic elements of an optical transmitter (laser, modulator, laser drive electronics, data drive electronics, sometimes temperature stabilization, data interfacing and control electronics and I/O interfacing, etc.) an optical receiver (photodetector, detector amplifier, possibly data and clock recovery, data and control electronics and I/O, and depending on application requirements and design specifications other electronics to perform physical layer protocol functions as well as functions to control these components. There are many applications for transceivers ranging from fiber to the home, to data centers to long haul and high-performance communications. The performance of the transceiver as well as its cost is tied to the particular application.
Today, most transceivers are manufactured in a pluggable form factor that can be installed and removed from a linecard or system without turning on and off the system power and allow the transceiver to be inserted and removed from a card cage slot. The pluggable modules often conform to a standard, like an XFP, QSFP+ or SFP package, and most recently CFP package, that includes electrical, optical and mechanical, or power dissipation/usage as well other factors that enable a modules to be purchased from different vendors to meet the needs of customers using these pluggables. However, non-standard form factors can also be implemented as well as construction of the transceiver directly on printed circuit cards, line cards, daughter cards or other form factor. Prior art array transceivers, including QSFP+ and CFP form factors, incorporate multiple transmitters and receivers in one package, each transmitting and receiving at a specified data rate. Those skilled in the art are familiar with the most common data rate per channel for arrayed transceivers are 2.5 Gbps, 10 Gbps 25 Gbps or other multiples used in the telecom or data communication industries or 1 Gpbs, 2 Gbps, 5 Gbps for other applications, are among the many examples. The lasers inside the arrayed transceiver are generally chosen for a particular application, for example for transmission over fiber lengths of 0 to several hundred meters will utilize VCSEL laser technology and VCSEL transceiver arrays are commonly used in large volume applications like communications within data centers.
Various designs that can be used in the fiber input/output of the transceiver array include a-fiber ribbon, with each fiber connected to each of the transmitters and receivers inside the arrayed pluggable. In this case, each laser in the array can be operating at the same optical wavelength (typically 830 nm or 1310 nm for short reach fiber distances), or the array may contain wavelength division multiplexing (WDM) where each transmitter emits light at a different wavelength. In the case of today's QSFP+ package, 4×10 Gbps channels are incorporated. Those skilled in the art are aware of standards for these various configurations described above, and other configurations that have been standardized. For short reach distances, less than 100 m, normally multimode fiber is used and the lasers operate at 830 nm, and a ribbon cable is used to connect to four transceivers within the QSFP+ pluggable. Those skilled in the art will be familiar with other designs and standards that support lasers each operating at the same 1310 nm, in which case there are ribbon fiber connectors for the input/outputs for each transceiver. In the WDM version, at 1310 nm, each laser is operating at a wavelength in the 1310 nm waveband, where the wavelengths have been set by standards bodies and multiple configurations can be used. For example, a ribbon fiber connecting the pluggable with a 1310 nm wavelength multiplexer/demultiplexer outside the QSFP+ package, multiplex/demultiplexes the wavelengths to/from a single fiber, or the wavelength multiplexer/demultiplexer is built into the package with only a single transmit and receive fiber connector interfaced to the package instead of a fiber array. In the later case of a 1310 nm configuration, a single mode fiber (SMF) is typically used.
Another recent form factor that supports arrayed transceivers is the CFP, a module that today contains 10×10 Gbps transceivers. The CFP, as with the QSFP+, can contain ten 830 nm VCSEL based transceivers connected to a ribbon connector at the CFP output to communicate over multi-mode fiber (MMF) at distances up to 100 m and sometimes 300 m. The CFP like the QSFP+ can also contain, for fiber distances from 100 m to 2 km or 10 km, identical 1310 nm transceivers connected to a ribbon for shorter distances (e.g. up to 300 m) or use the standardized 1310 nm 10 wavelength grid (as opposed to the 4 wavelength grid for the 40 Gps QSFP+ modules) that are multiplexed/demultiplexed, either internal to the CFP module or external.
For longer range transmission, fibers are today a scarcer commodity than in short reach transmission (e.g. under 2 km), although this can change in the future. To utilize as much bandwidth in the single fiber as possible, dense WDM (DWDM) is used with 1550 nm lasers operating with today, a channel spacing of 100 GHz according to the standard ITU grid. The CFP arrayed modules, for example, today contain arrays of fixed wavelength externally modulated lasers, most often using Distributed Feedback (DFB) WDM lasers, one wavelength for each channel inside the CFP. In order to fill up the bandwidth of a fiber, today's links are using 40 channels with 100 GHz spacing, which yields 400 Gbps per fiber, or 80 channels with wavelength spaced by 50 GHz for 800 Gbps, and higher capacities are used with more channels. Since the DFB lasers are fixed, a dedicated array of transceivers is needed for each set of channels per pluggable, for example 10 fixed wavelengths per 10 channel CFP. A dedicated CFP is then needed for each of the 10 channels, for example channels 1-10, 11-20, etc. This locks down the ability to use an array module to communicate on an arbitrary set of wavelengths or wavelength group and leads to many issues including the sparing problem, where a backup pluggable or array transceiver is needed to support each set of wavelengths. Additionally, the wavelengths output from each arrayed transceiver are fixed in the output wavelengths and therefore a client side electrical connection must be electrically rewired or switched to a different transceiver port to be transmitted over a desired wavelength or a desired group of wavelengths. This current use of fixed wavelength arrayed transceivers leads to cost inefficiencies in number of parts, parts tracking, sparing, and the ability to dynamically configure the output wavelength or group of wavelengths based on the connection or transmission needs of the network.
There is demand to push the fiber capacity to 1 Terabit per sec (Tbps) and beyond, so people are looking at DFB lasers that can operated on densely spaced optical frequency grids including 50 GHz grid, 25 Ghz grid, or narrower, integration of the laser with an external modulator for cost efficiency and power and space efficiency, and techniques that allow more data to be encoded on a given wavelength grid spacing including coherently optical modulation. One skilled in the art recognizes that while there are standards to operate systems at 50 GHz and 25 GHz grid spacing using incoherent or coherent coding, dedicated transceivers (non-arrayed) are typically used to reach this level of performance or in certain cases at the 1550 nm waveband, multiple fixed wavelength DFB lasers each designed to operate at a different optical frequency are used as a multi-wavelength array. Commercial arrayed transceivers today are of a fixed transmission wavelength only and do not afford the many benefits and advantages afforded by an array of tunable lasers transceiver. Examples of arrayed WDM transceivers available today include 4×25 Gbps fixed wavelength wavelength division multiplexed QSFP+ and CFP/2 or CFP/4 form factors, typically in the 1310 nm waveband and 10 channel fixed wavelength 100 Gbps 10 channel×10 Gbps transceivers employing fixed wavelength lasers some with and some without integrated optical data modulators. Other types of deployed arrayed transceivers use fixed wavelength lasers with coherent modulators. The CFP/2 and CFP/4 form factors refer to, as of yet, unstandardized small versions of the CFP form factor (½ width and ¼ width respectively), there are multiple efforts to standardize these form factors and other form factors continue to enter the market, however, all arrayed transceivers utilizing fixed wavelength laser.
Typically transceiver arrays are used to transmit aggregate data that has been converted to a parallel transmission format. This is the case where 100 Gbps Ethernet is transmitted over 10×10 Gbps wavelength channels, or 4×25 Gbps wavelength channels. These transceivers generally do not allow the flexibility to choose between aggregate transmission using all lasers or using each laser independently or subgroups of wavelengths in the arrayed transceiver for flexible parallel transmission.
Lastly, there is a current movement by several carriers and vendors to utilize not only a fixed wavelength grid but a flexible wavelength grid (discretized at some base spacing like 37.5 GHz) but allowing discretely arbitrary combinations of grids, modulation formats and channelization over the same fiber to co-exist in a flexible manner. This flexible grid concept will require new technology, components and system innovation, one example being a flexible grid reconfigurable optical add/drop multiplexer (Flex-ROADM) that is being introduced by several manufacturers. One example of a modulation format that can take advantage of a flexible grid, and is familiar to those skilled in the art, is the “superchannel” that places the wavelengths very close together to operate as a single transmission channel in order to send 1 Tbps and higher. This type of transmission requires filtering (multiplxing/demultiplexing) that is different than conventional DWDM or WDM transmission. See, e.g., “DWDM transmission at 10 Gb/s and 40 Gb/s using 25 GHz grid and flexible-bandwidth ROADM,” M. Filer and S. Tibuleac, National Fiber Optic Engineers Conference, Los Angeles, Calif., Mar. 6, 2011, Optical Switching and Nonlinear Management paper NThB.
There are several disadvantages and shortcomings of today's state of the art transceiver arrays and modules including, for example, today's arrayed 100 Gbps 10×10 Gps CFP modules utilize DFB lasers that are fixed in wavelength and todays 4×25 Gbps QSFP+ transceivers use 4 fixed wavelength lasers. The use of fixed wavelength lasers in each module results in CFP (or QSFP+ or any other arrayed module) to be built as fixed sub-bands, for example a module for wavelengths 1-10, a module for wavelengths 11-20, etc for dense wavelength division multiplexing, or as course wavelength division multiplexed links where for example the 4 25 Gbps channels, each on a different fixed wavelength in the 1310 nm waveband, are the only 4 wavelengths on the fiber. This use of fixed wavelength is expected to continue to new standards being develop for higher capacity transceivers, for example the 400 Gbs Ethernet under discussion among companies and standards body. However, this increase in bandwidth per fiber, and the need to fill the fiber capacity, and cost of sparing these modules has disadvantages described above. For example, for a dense WDM network where many channels are to be transmitted on a single fiber, these different modules are combined to load a fiber with as high a capacity as possible. If a module fails, then an identical module must be available as a spare, requiring many spare modules. Thus, the expense of upkeep of the system is increased with the number of spare modules. Also populating the fixed grid requires purchasing and installing the specific module for that planned to be used sub-band. Fixed wavelength modules also make it difficult to migrate from a certain channel grid (e.g. 100 GHz) to a new grid (50 GHz or 37.5 GHz for example). New modules must be purchased and installed, that either replace all modules with a new grid spacing, or are offset at the current grid spacing, and as known to one skilled in the art, interleaved with existing channels to create a new finer channel spacing (e.g. 100 GHz to 50 GHz). Thus, migrating from one channel grid to another is expensive in terms of labor and parts. Moving to flexible grid makes the issue even more complicated and costly as special modules must be used for each modulation format portion of the spectrum and these modules then combined (for example a superchannel set of modules combined with modules that transmit 100 G Ethernet or 400 G Ethernet).
Other needs for tunable arrayed transceiver modules, with each channel independently tunable, are to address a broader set of use cases for fiber optic communications and networks. For example, an array of 10 independently tunable transmitter inside an arrayed transceiver can be used to support 10 individual 10 Gbps transmission channels with each channel tunable to an available wavelength on the fiber. In addition to this flexibility, it is possible to package more channels in an arrayed transceiver than with individual packages, and using individually tunable channels within the array yields the same function as having separate tunable transceivers. This is a very important advance in the state of the art, as optical transceiver density is one of the main limitations to today's fiber systems.
Accordingly, there is a need for technology that allows for interchangeability between the components in an arrayed module such that the entire module need not be replaced when a component within the module fails. There is also a need for a technology which is adaptable to new channel grids without replacement of all modules and, in particular, adaptable to a flexible grid without replacement of all or substantially all the existing modules in the grid. Lastly, there is a need for modules that have the flexibility to serve multiple use cases, where the group of wavelengths inside the arrayed transceiver can be utilized as a single group of aggregate data, such as the case of the standardized 100 Gbps over 10×10 Gbps WDM channels, or using the channels individually in a higher density package.